After watching the rallycross episode of top gear again, I was wondering whats the cheapest way to go racing?

I was thinking in terms of racing a small hatch back on the odd weekend. Something where I can just turn up with the car, pay a fee, and race. Something I can do as a hobby rather than it taking over my life.

Ideally I'd like to be able to keep the car road legal, so that I can drive it to an from the track, with just a change of tyres for the journey.

Is there such a thing?

Edit.....I go karting once every couple of months, which is why I want to step up from that.